Electric Power Steering On-Center Feel Compensation
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Solution Overview
Problem
Electric power steering systems face challenges in maintaining the on-center feel due to excess friction and inertia, leading to differences in driving feel compared to conventional manual systems.
Innovation Solution
A control system that computes on-center torque adjustment compensation using a frequency-based methodology to compensate for the inertia of the steering actuator motor, generating a command signal to control the electric power steering motor based on sensed handwheel torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overall steering ratio is reduced to prevent friction interference with return-to-center function, then friction interference is reduced, but steering sensitivity increases excessively
Solution Approach 1:
The patent changes the steering ratio parameter dynamically based on steering angle. At large steering angles, a lower steering ratio is used to reduce friction interference and enable return-to-center function. At small steering angles near center, a higher steering ratio is used to reduce steering sensitivity and provide a more natural feel. This dynamic parameter adjustment resolves the contradiction between ensuring return-to-center function and maintaining appropriate steering sensitivity.
2Reliability
If electric power steering motor provides return-to-center force to overcome friction, then return-to-center function is achieved, but inertia and back EMF create notable difference in driving feel compared to manual systems
Solution Approach 1:
The patent applies preliminary action by pre-calculating and compensating for motor inertia and back EMF effects before they significantly impact the steering feel. The control system predicts the inertial effects based on current steering state and applies compensatory torque in advance, ensuring that the driver experiences a smooth, natural feel that closely mimics manual steering systems rather than feeling the artificial effects of motor inertia.
3Object-affected harmful factors
If near-zero torque assist command is applied at on-center position, then friction interference is minimized, but motor inertia and back EMF create artificial feel differences
Solution Approach 1:
The patent converts the harmful effects of motor inertia and back EMF into beneficial compensation signals. Instead of simply reducing torque assist to near-zero at on-center position (which leaves inertial effects unaddressed), the system calculates compensatory torque based on motor inertia and back EMF models, and adds this compensation to the torque assist command. This transforms the previously harmful inertial effects into a means of achieving more accurate and natural steering feel.
Data Source
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AI summary
A control system for controlling an electric power steering system is provided. The control system includes a first module configured to compute an on-center torque adjustment compensation based on a sensed handwheel torque. The on-center torque adjustment compensation is configured to compensate for inertia of a steering actuator motor using a frequency-based methodology. The control system also includes a second module configured to generate a command signal to control the steering actuator motor of the electric power steering system based on the on-center torque adjustment compensation.